Elevator safety system



Jan. 13, 1931.

D. LINDQUIST ELEVATOR SAFETY SYSTEM Filed March 1, 1927 3 Sheets-Sheet lINVENTOR ATTORNEY Jaln. 13, 1931. D. L. LlNDQ UlST v 1,789,008

ELEVATOR SAFETY SYSTEM Filed March 1, 1927 s sheets-sheet 2 40M) L. L"YINVENTOR BY. ATTORNEY Jan. 13, 1931. D. L. LINDQUIST ELEVATOR SAFETYSYSTEM Filed Mal ch l, 1927 3 Sheets-Sheet 3 ATTORNEY Patented Jan. 13,1931 UNITED STATES PATENT OFFICE DAVID L. LIND-QUIST, OF HARTSDALE, NEWYORK, ASSIGNOB TO- OTIS ELEVATOR COLT- PANY, OF-NEW YORK, N. Y., ACORPORATION OF NEW JERSEY IELEVATOR SAFETY SYSTEM Application filedMarch 1,

the stop may occur under such conditions as will result in the car beingretarded at a rate considerably in excess of gravity. Such a stop maycause considerable discomfort or possible injury to the occupants of thecar,

owing to the abruptness with which the can comes to rest. Furthermore,the counterweight will slow down at a lower rate than the car under suchconditions and, therefore, will continue its upward movement after thecar comes to rest. This continued upward movement of the counterweightafter the car has come to rest may occur also as a result of otherconditions under which the emergency stop occurs. Whenever suchcontinued upward movement of the counterweight takes place, slack willdevelop in the hoisting ropes, permitting the counterweight, upon comingto rest, to fall back. The counterweight, in falling, may developconsiderable kinetic energy by the time that the so slack developed hasbeen taken up.- As this kinetic energy is transmitted to the hoistingropes at the instantthey become taut, excessive and dangerous stressesmay result. Furthermore. this may result in the elevator car beingjerked upwardly and, as a consequence, in the occupants of the car beingsubjected to considerable shock if not actual injury. 7

When the counterweight, during its descent, is brought to anemergencystop, the stop may occur under such conditions that theelevator car slows down more slowly than the counterweight. In suchevent, the elevator car will continue its upward movement after thecounterweight comes to rest and thereafter fall back. Should the carsafety brakes riot act to stop the falling car before the slackdeveloped in the hoisting ropes is taken up, the car may come to such1927. Serial 1%. 171,739.-

Emergency stops also may occur under 7 such conditions, and with themoving bodies at such positions in the hatchway, that the Y ascendingbody may crash into the overhead work. This will not only cause damageto various'parts of the elevator installation but also, in the eventthat the elevator car is the 1 ascending body, may result in shockor'injury to the occupants of the car.

The object of the present invention is to caiise emergency stops to beeffected in such manner that the danger of shock or injury to theoccupants of the elevator car and the possibility of damage to theelevator installation is m nimized.

One feature of the invention resides in preventing excessive retardationof the descencling body of. an elevator system during an emergency stop.

Another feature ofthe invention is to prevent the continued ascent ofthe ascending body after the descending body has come to. rest.

Other features and advantages will become apparent fromthe followingdescripti on and appended claims.

The invention contemplates arranging the tensioning sheave for' thecompensating ropes in such manner that its upward movefunction as aclosed system during emergency stops. When an emergency stop occurs,therefore, not only are all the elements of this closed system retardedas a unit but the forces exerted on both the car and the counterweightsides act together on'the total mass of the system to effect theretarding action.

In carrying out the invention, according to the prefered arrangement,the tensioning sheave for the compensatingropesjs permitted freedom ofmovement in the down direction and a limited movement in the updirection for the purpose of takingcare of changes in the length of theelevator roping such as might be caused by temperature or humidityvariations or stretch o'f'the ropes.

In the drawlngs Figure 1 is a schematic representation of line 22 ofFigure 1;

rangement shown in Figure 1, parts being- Figure 3 is a view of a carsafety brake, this view being taken along line 3--3 of Figure 1 Figure 4is another view of the car safety brake shown in Figure 3, this viewbeing in partial sectin, taken along line 44 of Figure 1;

Figure 5 is a vlew in partial section taken along line 55 of Figure 4;

Figure 6 is a view in front elevation of the compensating ropetensioningsheave arshown in section;

Figure 7 is a view of the arrangement shown in Figure 6, taken alongline 7-7 of Figure 1, parts being broken away;

Figure 8 is an enlarged fragmental detail of one of the pawls shown inFigure 6;

Figure 9 is a view similar to Figure 7 of another arrangement forpreventing more than a limited upward movement of the tensioning sheavefor the compensating ropes;

Figure 10 is a top view of the arrangement shown in Figure 9, with partsshown in section;

Figure 1.1 is a view in section taken along line 11-11- of Figure 10;

Figure 12 is a view in section, taken along line -1212 of Figure 11; and

Figure 13 is a diagrammatic representation of an elevatorsystem-employed in explaining the invention.

Referring to Figure 1, the elevator car and counterweight 21 are raisedand lowered by means of the hoisting motor 22. An electromagnetic brake23 is provided for bringing the hoisting motor, and therefore the carand counterweight, to a stop. The hoisting ropes 24 for the car andcounter weight extend from the top of the elevator car over the hoistingsheave 25'on the motor shaft to the top of the counterweight.Compensating ropes 26 extend downwardly from the bottom of thecounterweight, around the tensioning sheave 27 in the elevator pit, andupwardly from this sheave to the bottom of the elevator car. Suitablearrangements for preventing more than a limited upward movement of thetensioning sheave will be described later. Guide shoes 28 are providedfor the elevator car and co-operate with the guide rails 30 to guide thecar in its movement up and down the hatchway. Sim ilarly, guide shoes 31are provided for the counterweight and cooperate with the guide rails 32to guide the counterweight in its movement up and down the hatchway.

The buffer for the elevator car is positioned in the elevator pit but isnot shown in Figure .1 as it would appear in front of the tensioningsheave 27 and would thus tend to obscure the arrangement of this portionof the elevator system. This buffer. however, is shown invFigure 7,being illustrated as an oil buffer and designated as a whole by thenumeral 33. The buffer 34 for the counterweight is shown in Figure 1.and is illustrated as an oil buffer and as suspended from thecounterweight. The bumper 29 for the counterweight buffer is indicatedin Figure 7.

Car safety brakes are indicated by numerals 35 and 36 and areillustrated as supported by the safety plank 37 of the 'car framework.These safety brakes are arranged to be operated in the event that theelevator car overspeeds by a certain amount during its descent, thisoperation being effected by means'of the governor 38. A plank switch 39is also supported by the safety plank 37 and is arranged to beoperatedwhen the safety brakes are applied. The governor is driven by theelevator car acting through the governor rope 40. The governor rope isattached to the arm 41 of a bell crank lever 42 pivoted on the carframework, with the other. arm 43 of the lever attached to a releasingcarrier 44, such arrangement being suitable for the type of safety brakechosen for purposes of description. The governor rope extends from itspoint of attachment around\ the governor sheave 45 and thence around atensioning sheave 46 in the elevator pit. This tensioning sheave isprovided with a tensioning weight 47 mounted inv uides 19.

In. causing the operation of tie safety 'bra-kes,the governor actsthrough a pair of jaws 48 and 50. Jaw 48 is arranged on one side of thegovernor rope, bein pivotally mounted in a bracket 49. Jaw 50 isarranged on the opposite side of the governor rope and is geared to jaw48. Jaw 50 is pivotally mounted on a pin extending through the yoked endof rod 51. Rod 51 is slidably mounted in a guide support 52 and isprovided witha spring 53. Jaw 48 is formed with an extension 54 to whicha link 55 of the governor is operatively attached. A

spring pressed latch 56 engages the extension 54 to maintain the Jaws 1nthe position illustrated during normal operation of the -bers 58 of thecar As shown in Figure 2, the lever 42 is piv-- oted on arod 57 suported by channel memamework. Arm 43 of lever 42 is secured to the lockbar 60 of the releasing carrier 44 as by a screw 59.v This bar iscarried by the releasing carrier bracket 61 secured to one of thechannel members. A boss 62 is formed on one side of the lock bar 60. Ajaw 63 is yieldingly maintained in a recess 64, formed in boss 62, bymeans of the spring 65. This spring is arranged-on a bolt 66 extendingthrough an aperture in the jaw 63, a slot in the lock bar and throughthe bracket and the channel to which the bracket is secured. Duringnormal operation of the car, the jaw 63 is maintained in the recess 64of the lock bar to maintain lever 42 in the position. shown in Figure l,in which positign the safety brakes are not operated. Upon the grippingof the governor rope with the car descending, however, the lever 42 isswung clockwise about its pivot to cause the operation of the safetybrakes, the lever being released by the lock bar 60 moving to the rightin Figure 2, forcing the jaw 63 out of recess 64 against the force ofspring 65. a

The operation of the safety brakes by .the above described movement ofthe lever 42 is eflectedthrough a lift rod 67. This rod is connected atits upper end to arm 41 of lever The operating lever is keyed to a rockshaft 69, this shaft extending across the car .to

safety brake 36 and being supported in bear; ings 70 formed on thesafety brake. housings 71. An operating lever 72' for safety brake 36 iskeyed to shaft 69 at the end opposite to that in which the operatinglever for safety brake 35 is secured.

In order that one of the advantages of the invention may be readilyunderstood, the safety brakes have been illustrated as of the type whichmay be released by upward movement of the car. ,These safety brakes areof similar construction and, therefore, only one 7 of them, namely,safety brake 35, will be described. The construction of this safet thebottom by a bracket 80 secured to the jaw member and being retained aainst the jaw member at the top by a stop p ate 81 secured ortion of awmember 73 to the housing 71 and extending into a recess 82 formed in thewedge. The wedge is free to swivel with respect to the jaw member, thebearing surfaces of the wedge and jaw member belng' semi-cylindrical, asindicated at 83,'to permit this movement. The-inclinedsurface of thewedge faces'the guide rail and is formed at its lower'end with adepression 84 to conform to the surface of the safety brake operatingroller 85. This roller is carried by a frame 86 pivotally mounted on aboss 87 formed on the end of lever 68 as by screws 88,. One of thesescrews also serves to connect the lift rod 67 to. lever 68. The uppersurface of boss 87 is abutted by roller 85, this surface being curvedand concentric" with the axis of pivot screws 88 so as to permit theroller to roll on this surface as the frame 86 swings on its pivot. Whenthe safety brake is not operated,- the lever '68 is supported by thebracket 80, this bracket being formed with a hooked portion 90 uponwhich the boss 87 rests. A bracket 91 is secured to the under surface ofjaw member'74 and extends to'the other side of the guide rail where itis formed with a beveled portion 92 extending parallel to the side ofthe guide rail. This beveled portion engages the roller 85 when thesafety brake is not operated, thus retaining the roller away from theguide rail end against the depressed surface 8410f wedge A releasingwedge 93 is carried by the portion of jaw member 7 4 opposite the guiderail 30. This portion of jaw member 74 is inclined upwardly toward theguide rail, the

inclined surface having a dovetail guideway- 94. The releasing wedge hasa dovetail tongue 95which fits into the guideway, thus 105 r permittinga sliding movement of the releasing wedge with respect to the jawmember. The sides of the guideway 94 and -the tongue 95 are of bearingmetal and are secured to theirrespectivelparts as by screws. Thereleasing wedge is urged upwardlywith respect to jaw member 74 by thecompression spring 96. This spring extends from a bracket 97 secured tojaw member 74 into a recess 98 7 formed in the releasing member,being-arranged on a' pin 100 secured to the bracket. A projecting web 99is formed on jaw member 74 and is adapted to engage an abutment 101 yformed on jaw member 73 when the safety brake is in released position.

A compression spring 102 is provided for causing the releasing wedge 93to engage the guide rail upon jaw member 73 being swung about shaft 75as a result of the engagement of roller 85 with the guide rail, as willbe explained later. This spring is arranged on a-bolt 103 between theends of the jaw membars 73 and 74 away from the guide rail. Spring 102may be placed under no initial compression or under any initialcompression that may be desired by varying the thickness of washer 112.The head bf this bolt extends into a square recess 105 arranged in jawmember 73, thus preventing the bolt from turning.

' A semi-annular web 106 formed on jaw memon a bolt 114 between an anglebar 115 and a washer 116 abutting against the head of the bolt. Theangle bar 115 is supported by another angle bar 117 secured to the.lower side of the safety plank 37. The bolt 114 extends through anaperture in angle bar 115 and through a similar aperture in a lug formedon jaw member 74. Nuts 118 are provided on the threaded end of bolt 114.By adjusting these nuts, the force exerted by spring 113 may be varied.This construction serves to maintain the jaw structure as a unit againststop plate 81. Thus stop plate8l not only serves as means formaintaining the wedge 78 against the jaw member 73 but also as a stopfor the jaw structure.

A cam 16 is secured to the rock shaft 69 (see Figure'l) The operatinglever 17 for the plank switch 39 is disposed in-the path of rotativemovement of the cam 16 so asto be engaged thereby during the rotativemovement of rock shaft 69 to effect the operation of the safety brakes.The plank switch is arranged in the control circuits for the hoistingmotor. 7

In operation, upon the occurrence of a predetermined overspeed duringthe descent of the car, the governor 38 operates, as previouslydescribed, to cause the jaws 48 and 56 to grip the overnor ro e, thuscaus ng the lever 42 to e released y the releasing carrier 44 and swungclockwise about its pivot.

to cause operating lever 68 of safety brake 35 to swing upwardly.Operating lever 72 of safety brake 36 is also swung upwardly as a resultof the movement of lever 42, being connected to operatin lever 68through rock shaft 69, as previous y described. As these safety brakes oerate in a similar manner, .the operation of only one of them, namely,safety brake 35, will be described.

As operating lever 68 swings upwardly 1t carries the roller 85 upwardlyalong the inclined surface of wedge 78 into engagement with the guiderail 30. The roller thereupon rolls on the guide rail and forces wedge78 away from the guide rail, thus causing jaw member 73 to swing aboutshaft 75. J aw member 73 acts through spring 102to cause 'aw member 74to swing about shaft 75, movmg releasing wedge 93 into engagement withThe lever 42 acts through lift rod 67 exerted by safety brake 36, causesthe car to i be brought to a stop.

As the levers 68 and 72 swin upwardly during the operation of the safetybrakes, cam 16, on rock shaft 69, engages operating lever 17 (see Figure1), effecting the operation of plank switch 39. The plank switch isarranged in the control circuits to act through electromagnetic switchesto effect the discontinuance of the supply of power to the hoistingmotor and the application of the electromagnetic brake to bring thehoisting motor, and therefore the hoisting sheave,

to a stop.

The safety brakes may be released'by bypassing the plank switch andenergizing the elevator motor'22 so as to move the car in the updirection. Considering only the action of safety brake 35, as brake 36is released in the same manner, during the initial move ment of the carin-the up direction, the releasing wedge 93 remains stationary on theguide rail, owing to the frictional force between this wedge and theguide rail. The inclined surface of jaw member 74 slides upwardly alongthe inclined surface of the releasing wedge and toward theguide rail,the jaw member thus swinging counter-clockwise about the shaft 75, asviewed in Figure 4. As a"'result, the spring 102 expands, de-

creasing the force exerted by roller '85 against the guiderail. Thefrictional forces exerted upon the roller by wedge 78 and the guide railbeing reduced, the roller rolls upon the guide rail and slides alongwedge .78 as the car moves upwardly. As' the roller moves away from thestop plate 81, the spring 102 further expands causing jaw member 73 toswing about shaft 75. The roller is brought to rest between bracket 91and the de ressed portion 84 of wedge 78 as the boss 87 engages thehookedportion 90 of bracket 80. As the roller moves onto the inclinedsurface 92 ofbracket 91, spring 113, being compressed, acts through bolt114 to cause the jaw member 74 to swing about shaft 75 in a direction toeffect the separation of the releasing Wedge 93 from. the guide rail. Asthis movement of jaw member 74 occurs, spring 96, having been compressedwedge abuts against the housing 71. Thus to slide upwardly along theinclinedsurface of the jaw member until the upper end of the the safetybrake isrestored to released position. During the releasing of thesafety brakes, the cam 16 disengages the operating switch to its normalposition. With both safety brakes released, the resetting of jaws 48 and50of the governor 38 and the replacing oft-he jaw 63 of the releasingcarrier 44 within the recess 64 of lock bar 60, places the system in itsoriginal condition.

The type of safety brake above described applies a practically .constantpressure against the guiderails throughout its'application. Theretarding force exerted, how-' ever, depends not only upon the pressureexerted against the rails but also upon the moothness of the rails, theamount of their lubrication and the kind of lubricant em ployed. Thesafety brakes are set in actual practice, therefore, so as. to havesufficient margin to stop the elevator car under the worst conditions,namely, with fully loaded car at the top of the hatchway, partedhoisting ropes, polished guide rails and excessive lubrication. Withsuch a setting, the safety in excess of gravity. This may result inbrakes may, under certain conditions, cause the car to be retarded at arate considerably discomfort and possibleinjury to the occupants of thecar. The'counterweight, owing to its kinetic energy, is retarded moreslowly than the-car under the above conditions and will continue itsupward movement after the ca r-comes to rest. Inasmuch as the tractiveeffort of the hoisting sheave, acting through the hoisting-ropes assiststhis kinetic energy 2f the counterweight, as will be seen from laterdescription, the-extent of the continued upwardmovement of thecounterweight may be considerable. Slack will develop as a re-.

sult of the continued upward movement of he counterweight, permittingit, upon coming to rest, to fail -..back. Although friction between theropes and the hoisting sheave may prevent a free fall, nevertheless,unless the amount of slack is small, the falling counterweight will haveattained considerable speed at the instant the ropes become taut and theresulting shock will cause excessive stresses. Furthermore, the shockwill be transmitted through the hoisting ropes to the car, causing therelease of the safety brakes and considerable discomfort if not injuryto the occupants of the car. As the length of the compensating ropes isfixed, the counterweighhin order to continue 1ts upward movement afterthe car has come to rest, must lift the compensating rope tensioningsheave. If the lifting of this sheave is prevented, the slowing down ofthe counterweight at a lower rate than the car and, therefore, thecontinued upward movement of the counterweight after the car has".

, for any contractionof the roping due to term lever '17 of plank switch39, restoring this perature and humidity changes.

A suitable arrangement for preventing more than a limited upwardmovement of the tensioning sheave for the compensating ropes is shown inFigure 1 and is illustrated in detail in Fi ures 6' and 7. Referringparticularly to F sheaveis mounted on ball bearings 120 positionedbetween sleeves 121 arranged on shaft 122. Grooves 123 are providedaround the periphery of the sheave for the compensating ropes 26. Asonlyjwo compensating ropes and two hoisting ropes are shown in' Figure 1for convenience of illustration, the

tensioning sheave is shown with only two' V and 126. These guidescooperate with the. inner legs 129. of the vertical angle bars 130 and131'to guide the frame124, aiid therefore the sheave 27, during anymovement thereof that may occur. The angle bars 130 and 131 are securedat the bottom to an angle bar 132 bolted to the floor of the elevatorpit. Angle bar 130 is secured at its top to igures 6 and 7, thetensioning A portion of the inner leg 1290f vertical angle bar 130'adjacent the top of tensionin sheave frame 124 is serrated to form arac137. The portion of the inner leg 129 of vertical angle bar 131 oppositethe rack 137 is also serrated to forms. rack 138. A pawl 140 for rack137 is ivotall mounted on a shaft 141 supported y two ugs 142 formed onthe top of frame p.0rtion125. Similarly, a pawl 143 for rack 138 ispivotally mounted on a shaft 144 supported by two lugs 145 formed on thetop of frame portion 126. These pawls are formed so'that their weightstend to cause them to turn outwardly about their pivot shafts and, asaresult, the operating ends of the pawls are maintained in cooperativerelation with their respective racks.

Also, each pawl is constructed so as to be flat on the bottom (seeFigure 8), this flattened portion cooperating with the tensionand 147respectively with the compensating teeth of their respective racks.

ropes taut. Assume further that, as a result of stretching of ropes,slack tends to develop in the compensating ropes. As this stretchingtakes place the tensioning frame and sheave, owing to their weight, movedownwardly, guided by angle bars 130 and 131, keeping the compensatingropes taut. As this downward movement occurs, the pawls 140 and 143 willbe moved inwardly about their pivots by the rack teeth 148 and 150respectively. Upon the disengagement of the ends of the pawls and theteeth 148 and 150, the pawls will swing outwardly under the influence ofgravity until their flattened portions engage the top of the tensioningsheave frame, this being the position of parts illustrated in'Figure 6.In the event of further downward movement of the tensioning sheave andframe, the pawls will act in the same manner with respect to' the nextlower This rack and pawl arrangement permits limited upward movement ofthe tensioning sheave and frame, even under the conditions Where thepa'wls have ust moved into a new tooth slot, owing to the fact thatthere is clearance between the top of these pawls and the bottom of therack teeth next above, as illustrated by the position of parts in Figure6. Thus, the tensioning sheave and frame may adjust themselves to anychanges in the length of the elevator roping due to temperature andhumidity variations.

Should the operation of the safety brakes occur under such conditionsthat the counterweight tends to retard more slowly than the elevatorcar, a force is exerted tending to lift the compensating rope tensioningsheave, causing the engagement of the pawls with the bottom of the rackteeth next above them. Upon the engagement of the pawls and rack teeth,any .further upward movement of the tensioning sheave is prevented. Thecar and counterweight, therefore, are retarded as a unit and come to astop simultaneously. Thus, as the continued upward movement of thecounterweight after the car has come to rest is prevented, thecounterweight can fall back at the most only an amount corresponding tothe slack developed in the hoisting ropes during the stop. This slack,however, is necessarily small owing to the limited upward movement ofthe tensioning sheave allowed for contraction of roping.-

Thus, no shock results when this small,

amount of slack is taken up and, therefore, the danger of seriousstresses, release of the safety brakes and shock or injury to theoccupants of the car is eliminated.-

Owing to the fact that the outward swinging movement of the pawls abouttheir pivots is limited by the engagement of their fiattened bottomportions with the top of the tensioning sheave frame, the pawls areprevented from appl ing lateral thrusts to the anglebars upon tcuengagement with rack teeth as a result of a lifting force beingapplied to the tensioning sheave. Thus, the

spreadin of the angle bars is prevented As soon ast e lifting forcedecreases sufliciently,

the tensioning sheave again becomes free to take up slack in theelevator .ro ing.. Another arrangement suitab e for preventing more thana limited upward movement of. the tensioning sheave is illustrated inFigur'es 9 to 12 inclusive. The arrangement of. the tensioning sheave149 and frame 179. is the same as previously described, the frame beingprovided with guides 128 for cooperation with the inner legs 151 of thevertical-f angle bars 152 and 153. A cross-head 154 is arranged abovethe frame 179, being sup. ported by means of compression springs 155 and156 extending from the top of the frame into recesses 157 and 158respectively formed -in the cross-head. Lugs are formed in the recessesfor positioning springs 155 and 156 are arranged within opening 161, oneon each sideof the leg of angle bar 153. The wedge block 162 isositioned in a slot 164 providedin the, crossead at the side of opening161 and is provided with a projection 165. This projection extends intoa recess 166, the wedge block being secured to the cross-head as by ascrew 167 extending through the cross-head into the projection. Thewedge block 163 is secured to the cross-head in a similar manner, beingpositioned in a slot 168. The inclined surfaces of these wedge blocksface the sides of the leg 151. Between the wedge blocks and the side ofleg 151 are arranged a pair of wedges 170 and 171. The sides of slot 164and the projection 172 formed on wedge block 162 serve as retainers forwedge 170 while the sides of slot 168 and a similar projection 173formed on wedge block 163 serve as retainers for wedge 171. Wedge blocksand wedgesare arranged within the opening 160. As the arrangement ofthese Wedges and blocks is the same as described for wedges 170 and 171and blocks 162 and 163, no detailed description of this portion of themechanism will be given.

A portion 174 of the cross-head is formed to extend around the leg 175of angle bar 153. This portion 174 and the portion 176 of the cross-headon the other side of the angle bar are connected by a plate 169, securedthereto as by screws 177. The portions 174 and 176 extend slightlybeyond the back side of leg 175, thus providing clearance between theplate and the angle bar. The portion 176 of tlltLQIOSS-l'RRd projectsdownwardly along the back side of leg 151' while portion 174 projectsdownwardly along leg 153'. Thesep'roj ections are connected at thebottom by a plate 1.78, secured thereto as by screws 180. Thisarrangement is such that there is a slight clearance between the plateand the back side of leg 175. Webs 181 are provided for strengtheningthese projections. As the other "nd of the cross-head is arranged in thesame manner, the arrangement will not be described.

The above described arrangement permits the tensioning sheave and frameto move downwardly to take up any slack in the compensating ropes. Thecross-head 154 moves downwardly along with the tensioning sheave andframe, the wedges being released sufiiciently to permit this movement.The wedges follow along with their wedge blocks during this downwardmovement, .thus being constantly in engagement with the sides of thelegs 151 of the angle bars. Any appreciable upward movement of thecross-head, however, is prevented. Upon an upward force being applied tothe cross-head, the resulting slight upward movement of the wedge blocksforces the wedges into clamping engagement with legs 151 of angle bars152 and 153, preventing any further upward movement. There is clearance,however, between the'topof the tensioning sheave frame and theprojection159. Thus,althoughupwardmovement of the cross-head isprevented, the tenvd'oning sheave and frame may move upwardly a shortdistance against the force of springs'155 and 156. This limited upwardmovement permits the sheave and frame. to adjust themselves to anychanges in length of elevator roping due to temperature and humidityvariations.

Should the operation ofthe safety brakes occur under such conditionsthat the counterweight tends to retard more slowly than the elevatorcar, aforce is exerted tending to lift-the tensioning sheave and frame.Upon 'this lifting force being applied, the tensioning sheave and framemove upwardly, com- 65,pre .si ng springs 155and 156, into engagementwith projection 159. The wedge blocks act, upon this upward force beingtransmitted to the crosshead, to force their wedges into clampingengagement with the angle bar legs'151, thus preventing any furtherupward movement of the cross-head, and, therefore, of the 'tensioningsheave and frame. The car and counterweight, therefore, are slowed downas a unit and come to a stop simultaneously. Thus, as continued upwardmovement of the counterweight after the car has come to rest isprevented, the counterweight can fall back only an amount correspondingto the slack developed in the hoisting ropes, which slack is necessarilysmall owing to the limited upward movement of the tensioningsheaveallowed for contraction of roping. Thus, v.no shock results when thissmall amount of slack is taken up and, therefore, the danger of seriousstresses,-release of the safety brakes and shock or injury to theoccupants of the car is eliminated. 1

The plates 169 and 178, and their eorre-' sponding plates on the otherend of the crosshead, act to prevent any skewing of the crosshead, uponupward forces being applied, as might otherwise take place as a resultof unequal clamping actions on the two legs 151. As soon as the liftingforce decreases sufficiently, the tensioning sheave and frame movedownwardly untilthe roping becomes taut. Springs 155 and 156, therefore,expand and, as the upward pressure against the crosshead is relieved,the cross-head becomes free to move downwardly of its own weight. Theinclined surfaces of the wedges and their cooperating wedge blocks aresuch as to insure not only the clamping of thewedges against 'the anglebar legs 151 upon an upward force being applied to the cross-headbutalso the releasing of the wedges upon this pressure being relieved.Thus, as the upward pressure against the cross-head is relieved, .the

wedge blocks slide downwardly on the in clined surfaces of'theirrespective wedges, thus relieving the pressure of the wedges against thelegs 151, the cross-head being brought to rest by the springs 155 and156.

It is to be understood that other arrangements may be employed toprevent upward movement of the tensioning sheave. Owing to the fact thatsuch arrangements act in effect to tie down the tensioning sheave, forconvenience of further description, t he tensioning sheave willhereinafter be referred to as tied down.

Should the emergency stop occur under such conditions that thecounterweight tends to slow down at a higher rate than the car, suchunequal retardation also is' prevented,

owing to the fact that the hoisting sheave system is diagrammaticallyshown.

Let

C=the weight in lbs. of the empty car, L= the weight in lbs. of the loadin the car, W= the weight in lbs. of the counterweight, R =the weight inlbs. of one-half of the elevator roping, the weight of the roping on"ach side of the hoisting sheave being equal regardless of the positionof the car and counterweight in case of complete compensation, hereassumed,

R '=the weight in lbs. of that portion of the hoisting ropes between thetop of the car, point no, and the oint b at the hoisting sheave,

S=the retarding force in lbs. of'the safety brakes,

T =the rope tension in lbs. at the point I),

T '=the rope tension in lbs. at the point (1, and

a =the acceleration in feet per sec. per sec.

Although theiequation which Wlll be developed for the closed system isapplicable to all emergency stops during which the counterweight tendsto slow down more slowly than the car, actual calculations foracceleration will be made only for conditions wherein the car in asystem in which the compensating tensioning sheave is not tied down,would tend to slow down at a rate in excess of gravity.

Certain factors, such as the weight of the tensioning sheave and frame,the weight of the control cables and the mechanical friction of the carand counterweight on the guides will be neglected, as this may be donewith this direction will be considered as positive.

The acceleration of the system as a result of the application of thesafety brakes may found from Newtons basic formula F=Ma 1 as previouslyexplained, causes the 'discontinuance of the supply of power to thehoist-' ing motor and the application of the electromagnetic brake tobring the motor and the hoisting sheave to a stop. Owing to the timeelements of these electromagnetic switches and of the electromagneticbrake and the Y inertia of the rotating parts of the hoisting apparatus,the circumferential speed of the hoisting sheave will be greater thanthe rope speed during the emergency stopping operation. Thus slipping ofthe hoisting ropes results. During this slipping of the hoisting ropes,the hoisting sheave exerts a frictional force upon the ropes, producinga tractive effort in the direction of motion. Owing to this tractiveeffort, the tension T at'the point d is greater than the tension T atthe point 6. According to the theory of equilibrium of a perfectlyflexible and non-extensible band in contact with a sheave, there existswhile slipping occurs the following relation between T, and T T2=KT1 2 iin which K is the traction relation and is a quantity greater thanunity. This quantity varies between certain limits but is generallyassumed in elevator calculations as 2. Thus Under stopping conditionswhere the counterweight tends to'lift the tensioning sheave forthecompensating ropes, owing to the fact that a limited upward movementof the tensioning sheave is permitted, there will be a tendency forslack to develop in the hoisting ropes at the point :0, slackbeingindicated in Figure 13. The tension in the ropes at point w,therefore, will be zero.

Applying Newtons law to determine the value of T T2 2R), T0, As theacceleration of all the elements of the closed system is the same, theacceleration may be found by considering any portion of the system. Theforce existing at point at now being known, the acceleration will becalculated by considering that portion of the system extending from thetop of the car, point 11:, down around the tensioning sheave and up tothe point d. The summation of the forces for this portion of the systemis Substituting the value of T as found in Equation (4) and simplifyingF=-'s+0+ -R,,-.W+2R,,- a

The summation of the masses for this portion of the system isTransposing and simplifying Before assuming actual values andcalculating the acceleration for the closed sys tem, an equation will bederived for acceleration in a system wherein the tensioning sheave isnot tied down, under conditions where the car is retarded as a result ofthe application of the safety brakes at a rate in excess of gravity.Owing to the fact that the tensioning sheave is free to move upwardly insuch system, the weight and mass of the counterweight, the weight andmass of the roping on the counterweight side of the hoisting sheave andthe weight and mass of the roping above the car on the car side of thehoisting sheave are not factors to be considered in deriving thisequation. Thus,'considering the direction of motion as positive asbefore, the summation of the forces is y 9 v fa, being employed todesignate the acceler- 'ation to distinguishfrom a in the closed system.Thus N ow let it be assumed that C 4000 lbs,

L 3000 lbs. (full load), VV= 5200 lbs.,

R 1500 lbs., and

S 12000 lbs.

Consider first the condition of empty car, with the car suflicientlynear the bottom of the hatchway when the safety brakes operate that Rmay be considered equal to R with only small error. In the systemwherein the tensioning sheave is not tied down, the acceleration may befound by substituting the assumed values in Equation (10). Thus a12000+l000+0+1500v 1500 Under such conditions, therefore, the car isretarded at twice gravity rate which is rather excessive. Thecounterweight, however, slows down at a rate less than gravity, owing tothe fact that the tractive effort of the hoistmovement of thecounterweight after the car comes to rest, therefore, may beconsiderable.

As the counterweight is retarded at a lower rate than the car" under theabove conditions, when the tensioning sheave is not tied down, Equation(7) for the system wherein the tensioning sheave is tied down isapplicable.

Substituting the assumed values in Equation (7) of thecounterweightafter the car'has come to rest.

Next consider the condition of empty car, with the car sufiiciently nearthe top of the hatchway when the safety brakes operate that R, may beconsidered equal to 0 with only small error. In the system wherein thetensioning sheave is not tied down, the acceleration, according toEquation (10) with the assumed valued substituted, becomes f4000+0+1500-0 or i g 6500 .a1 g 1.1829

The counterweight will slow down at gravity 12200 13829 Thus, althoughthe rate at-which the car is retarded under the assumed conditions isnot excessive with or without the tensioning sheave tied down,nevertheless this rate is less when the tensioning sheave is tied downthan when it is not.

It will be seen from the above examples that the rate at which the caris retarded varies according to the position of the car in the hatchway.The load in the car, as shown by Equations (7) and (10) is anotherfactor upon which the rate of retardation depends. As an example, assumethat the car is at such position in the hatchway that Rh= 1200 lbs. andL=500 lbs. Substituting theassumed values in Equation (10) Thecounterweight, however, will slow down at less than gravity rate, owingto the trac tive effort of the hoisting sheave.

As the counterweight is retarded more slowly than the car under theassumed conditions, when the tensioning sheave is not tied down,Equation (7) for the system wherein the tensioning sheave is tied downSubstituting the values as- Thus, under the conditions assumed, the caris retarded at a rate less than gravity when the tensioning sheave istied down while, when the tensioning sheave is not tied down, the car isretarded at a rate one and one-half times gravity.

It is believed that the above examples are suflicient to show that, in asystem wherein the tensioning sheaveis tied down, excessive retardationof the car is prevented.

In the above examples it was assumed that the hoisting ropes wereintact. Should the hoisting ropes part, with the elevator cardescending, the elevator car becomes a 'freely falling body, unless,somewhat retarded by the dragging of the hoisting ropes over thehoisting sheave. The governor ropes, therefore, owing to their inertia.and the inertia of the governor and governor rppe tensioning sheave,cause the immediate operation of the safety brakes. Assume that thehoisting ropes part at the top of the car, point an. Considering thesystem with the tensioning sheave for the compensating ropes not tieddown, so long as the conditions, such as the amountv of load andposition of the car in the hatchway, are such that the counterweightretards more slowly than the car, the car is retarded at the same rateas ifthe roping were intact. Similarly, in the, case of the system withthe tensioning sheave tied down. so long as the conditions, such as theamount of load and the position of the car in the hatchway, are suchthat the tension at point 00- during the stop would be zero if the ropeswere not parted, the car is'retarded at the same rate as if the ropeswere intact.

Assume next that the hoisting ropes part at some other point, forexample, at the top of the counterweight, with the ca r descending asbefore. In the system herein-the tensioning sheave is not tied down.with conditions such that the counterweight retards more slowly than thecar, the car is retarded at the same rate as if the roping were intact\Vith the tensioning sheave tied down, however, although the rate atwhich the car is retarded is not thesalne as it the ropes were intact,nevertheless, excessive retardation of the ear is prevented. It isbelieved that: this 1 maybe made clear by a single example. Assume emptycar, with the car descending and near the top of the hatchway when theropes part. The summation of the forces for this condition is s+o+ R-1a, w The summation of the masses is I M QHRfZhlTW g Therefore, theacceleration is elements Thus the car is retardedat a rate only slight.-ly in excess of gravity.

Should the ropes part with the car ascending, the car will come to restand then start to fall. The falling car is retarded at the same rateunder such conditions, regardless of whether the tensioning sheave istied down or not. Assume that the car isascending fully loaded and isnear the top of the hatchway and that the hoisting ropes part at thepoint x. The car will continue its upward movement for a short distanceand thereupon start to fall. \Vith the safety brakes applied thesummation of the forces exerted to stop the falling car is Substitutingthe values assumed for these elements 3500 a g 0.412g

The car is retarded, therefore, at less than half gravity rate. Thisexample also illustrates the fact that the retarding force assumed forthe safety brakes has ample margin to insure the stopping of the carwhen the hoisting ropes part under the worst conditions as regards theamount of load and position of the car in the hatchway.

In the above examples it was assumed that the operation of the safetybrakes was eft'ected either by the governor upon the occurrence of apredetermined amount of overspeed during the descent of the car or owingto the inertia of the governor apparatus in the event of the parting ofthe hoisting ropes. It is to be understood, however, that the tying downof the tensioning sheave is effective to prevent excessive retardationof the car and continued upward movement of the counterweight after thecar has come to rest, regardr less of the mechanism effecting theoperation of the safety brakes or the conditions in response to whichthe operation of the safety brakes is effected. Furthermore, althoughthe emergency stops have been described as ef fected by safety brakes ofa certain type, it is to be understood that, with the tensioning sheavetied down, excessive retardation of the car and continued upwardmovement of the counterweight after the car has come to rest isprevented when the emergency stop is effected by other forms of safetybrakes I or by the car buffer or other safety apparatus.

Also, with the tensioning sheave tied down, the system will act in thesame manner, when the counterweight is the descending body and isbrought to an emergency stop, as has been described for emergency stopswith the car the descending body. Thus, should the counterweight bebrought to an emergency stop by the engagement of its buffer with the.

bumper block 29, by the operation of counterweight safety brakes, ifprovided, or by the operation of other safety apparatus, upward movementof the car after the counterweight has come to rest is prevented. Infact, the

- tying down of the compensating rope tensioning sheave preventsexcessive retardation of the descending body during stopping andcontinued upward movement of the ascending body after the descendingbody has come to rest, regardless of the agency causing the stoppingandregardless of the conditions under which the stopping occurs.

In theevent that compensating ropes are not provided, it is to beunderstood that roping or the like may be extended downwardly from theelevator car, around a sheave and then upwardly to the counterweight, ina manner similar to the arrangement of compensating ropes,'with upwardmovement of this sheave prevented by arrangements such as previouslydescribed.

What is claimed is:

1. An elevator system comprising; a an elevator car; a counterweight;hoisting mechanism for said'car and counterweight,

said mechanism including hoisting roping; safety means for stopping saidcar, said safety means having sufiicient retarding force to insure thestopping of the car under conditions where the car is fully loaded andnear the top of the hatchway with the hoistroping parted; and means forprevent ing said safety'means causing excessive retardat ion of the car,regardless of the conditions under which the stoppingoccurs.

'2. An elevator system comprising; an elevator car; a counterweight;hoisting mechanism for said car and counterweight, said mechanismincluding hoisting roping; roping for compensating for the unbalancedweight of said hoisting roping; a tensioning sheave for the compensatingroping; safety means for stopping said car, said safety means havingsufiicientretarding force to insure the stopping of the carunder-conditions where the car is fully loaded and near 7 the top of thehatchway with the hoisting roping parted; and'means for preventing aidsafet means causingv excessive retardation of the car, regardless of theconditions under which the stopping occurs, said last included meanscomprising means for preventing more than a limited upward move- :nentofsaid tensioningsheave.

3. The combination of a car and a counterweight therefor, a compensatingcable connected between the car and the counterweight and running undera sheave, a weight connected with said sheave, vertical guides in whichthe weight is free to move, and means interposed in the path of movementof the weight arranged to limit the upward movement thereof. 1

4. The combination of a car and a counterweight therefor, a compensatingcable connected between the car and the counterweight and running undera sheave, a weight connected with said sheave, vertical uides in whichthe-weight is free to move, a ar movable on the guides arranged to limitthe upward movement of the weight, and means for locking the bar againstupward movement.

5. In a traction elevator, a car and a counterweight arranged to run ina hoistway, a driving sheave at the upper end of the hoistway, a secondsheave at the lower end of the hoistway, a cable system forming A withsaid car and counterweight an endless connection between. said sheaves,a weight connected with said sheave, vertical guides for the weight, abar movable on the guides arranged to limit the upward movement of theweight, and means for locking the bar against upward movement.

In testimony whereof, I have signed m name to this specification.

DAVID L. LINDQUIST.

